http://www.cplusplus.com/reference/cstdlib/free/

free

void free (void* ptr);

Deallocate memory block

A block of memory previously allocated by a call to malloc, calloc or realloc is deallocated, making it available again for further allocations.

If ptr does not point to a block of memory allocated with the above functions, it causes undefined behavior.

If ptr is a null pointer, the function does nothing.

Notice that this function does not change the value of ptr itself, hence it still points to the same (now invalid) location.

Parameters

ptr: Pointer to a memory block previously allocated with malloc, calloc or realloc.

Return Value

none

Example

/* free example */
#include <stdlib.h>     /* malloc, calloc, realloc, free */

int main ()
{
  int * buffer1, * buffer2, * buffer3;
  buffer1 = (int*) malloc (100*sizeof(int));
  buffer2 = (int*) calloc (100,sizeof(int));
  buffer3 = (int*) realloc (buffer2,500*sizeof(int));
  free (buffer1);
  free (buffer3);
  return 0;
}

Edit & Run

This program has no output. It just demonstrates some ways to allocate and free dynamic memory using the C stdlibfunctions.

Data races

Only the storage referenced by ptr is modified. No other storage locations are accessed by the call.
If the function releases a unit of storage that is reused by a call to allocation functions (such as calloc or malloc), the functions are synchronized in such a way that the deallocation happens entirely before the next allocation.

Exceptions (C++)

No-throw guarantee: this function never throws exceptions.

If ptr does not point to a memory block previously allocated with malloc, calloc or realloc, and is not a null pointer, it causes undefined behavior.

free 释放内存